If the mind is happy, the entire world (seems) happy. If the mind is despondent, the entire world (seems) despondent. Hence, if you desire happiness, strive towards the happiness of the mind first.

Commentary:

By definition, mind, is the set of cognitive faculties that enables consciousness, perception, thinking, judgement, and memory. It is a subtle body, meaning, it cannot be felt through the 5 gross sense organs. It is perceived, by oneself! Anyone can only try to understand another's mind, but total perception is available only to the self. In another subhaaShita, it is said, that which is in one's mind cannot be perceived even by Lord brahma, the creator! Such is the intricacy of mind.

Now that the complexity of the mind is established, what is it's role in influencing the outlook of a person? Well, it is as simple as - if the mind is happy, the world looks happy and cheerful; if the mind is sad, the world looks sad and morose! The same exact world around the person, can look an entirely opposite shade, if the mind is not cheerful! Obviously, who wants sadness? Everyone wants to live in a happy and peaceful world. The author says, in that case, first work towards keeping your mind happy! Now, how is that achieved? By having a positive outlook at life. By trusting that there is someone above watching at all times and whatever He is bringing to one's life, it is for one's own betterment. Positive attitude keeps the mind merry. A child is happy and he does not need a reason for that! If that kind of an outlook is developed by us adults, then the world truly would be such a beautiful place. No one would need doctors for any ailments, because, a healthy mind has a healthy body. The state of one's mind influences one at all levels - body, mind, spirit.

Hence to be a well rounded person, it is all the more essential to strive towards keeping the mind cheerful and positive. Stay happy, understand life!